AMS Dating Higham

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RADIOCARBON, Vol 48, Nr 2, 2006, p 179195 2006 by the Arizona Board of Regents on behalf of the University of Arizona

179

AMS RADIOCARBON DATING OF ANCIENT BONE USING ULTRAFILTRATION

T F G Higham1,2 R M Jacobi3 C Bronk Ramsey1

ABSTRACT. The Oxford Radiocarbon Accelerator Unit (ORAU) has used an ultrafiltration protocol to further purify gelatinfrom archaeological bone since 2000. In this paper, the methodology is described, and it is shown that, in many instances,ultrafiltration successfully removes low molecular weight contaminants that less rigorous methods may not. These contami-nants can sometimes be of a different radiocarbon age and, unless removed, may produce erroneous determinations, particu-larly when one is dating bones greater than 2 to 3 half-lives of14C and the contaminants are of modern age. Results of theredating of bone of Late Middle and Early Upper Paleolithic age from the British Isles and Europe suggest that we may needto look again at the traditional chronology for these periods.

INTRODUCTION

Despite its obvious appeal to archaeologists, most radiocarbon facilities date bone only rarely. Theprincipal reason may be the often poor preservation of collagen in many contexts. Equally, however,there has been a traditional skepticism concerning the reliability of bone 14C determinations amongarchaeologists (Burky et al. 1998), despite the obvious attraction of bone as a dating substrate that

is usually related to the archaeological event rather well. Preservation of bone collagen is influencedprincipally by the environment within which the bone is deposited, and, specifically, by the interre-lated influences of pH, microbial activity, temperature, and water. However, these diagenetic influ-ences can be extremely variable between, and within, sites (von Endt and Ortner 1984; Hedges andMillard 1995; Holmes et al. 2005). In general, there is a broad gradient in the preservation state ofbones from those deposited in warmer, more humid environs to those recovered from archaeologicalcontexts in colder, more temperate climes. Over many years, it has become apparent that the char-acterization of the quality of the extracted collagen is crucial to validate the accuracy of theobtained 14C determinations. Several methods of achieving this have been described (e.g. DeNiroand Weiner 1988a; Ambrose 1990; van Klinken 1999), but few 14C laboratories regularly apply therange of analytical measurements necessary to provide minimum assurance for submitters of bonesamples (e.g. C to N ratios) even when the samples are of crucial importance to studies of latehuman evolution (e.g. Wildet al. 2005).

Bone collagen (we follow DeNiro and Weiner 1988; van Klinken 1999; and Hedges and vanKlinken 1992 in using this term) is uniformly targeted for 14C dating because it is the preeminentprotein, and indigenous bone carbonate (hydroxyapatite) is so far inseparable from diagenetic car-bonate. Individual collagen molecules contain 3 polypeptides that each comprise about 1000 aminoacids per chain (alpha chains). These are arranged in fibrils, twisted into a right-handed coilweighing between 95 and 102 kD (1 kD = 1000 amu [atomic mass units] where 1 amu = 1/12 massof 1 12C atom). The most commonly applied pretreatment protocol is the so-called Longin collagenmethod in which collagen (the insoluble residue remaining after decalcification of the bone) isfirst isolated by decalcification, then denatured in weakly acidic water (gelatinization), untwistingthe triple-helical collagen molecule and thereby reducing the influence of insoluble residues (Lon-gin 1971). In many cases, this method produces gelatin that enables reliable 14C ages to be deter-mined, but it is difficult to validate with confidence the exclusive removal of exogenous carbon to

1Oxford Radiocarbon Accelerator Unit, RLAHA, Dyson Perrins Building, University of Oxford, Oxford OX1 3QY, UnitedKingdom.

2Corresponding author. Email: [email protected] of Prehistory and Europe, Franks House, The British Museum, London N1 5QJ, United Kingdom; also Depart-ment of Palaeontology, Natural History Museum, London SW7 5BD, United Kingdom.


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180 T F G Higham et al.

low levels (about


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AMS 14C Dating of Ancient Bone Using Ultrafiltration 181

DATING ANCIENT BONE USING ULTRAFILTRATION

Since ultrafiltration was adopted at ORAU, a larger number of accelerator mass spectrometry(AMS) determinations 31,000 BP) have been obtained (Figure 1) than was previ-

ously the case. Pretreatment chemistry is of key importance, as described below, but other develop-ments are also considered relevant. Reductions in measurement background and increasing levels ofmeasurement precision have been achieved during the same period (Bronk Ramsey et al. 2004b).Since 2000, the range and breadth of standards specific to the sample type we most regularly date,which is bone, have been widened. The additional standards routinely dated include:

Two bison bones from Alaska assessed to be >60 kyr in age on the basis of multiple AMS repeatdates;

Pig (Sus scrofa) rib bones from the Mary Rose (the flagship of Henry VIII, which sank inAD 1545).

In addition, we have also introduced a further standard:

Mammoth bone ~40 kyr BP, a partial pelvis recovered from the Quartz Creek site, Alaska. Cur-

rently, this is being used for the VIRI intercomparison (sample E).

The >60-kyr BP standards (2 bison bones from Alaska) are used as blanks and regularly analyzed toquantify a background correction to account for chemical pretreatment processing of bone (BronkRamsey et al. 2004a). Low and high mass amounts of bone are regularly pretreated and dated. Lowmass is defined in this instance as the lowest starting weight from which we can obtain enough col-lagen for a ~1.7-mg graphite sample (i.e. 45 mg ultrafiltered gelatin). When these bison bones arecorrected for graphitization and machine background, the results show that for bone >10 mg ultra-filtered gelatin (our minimum extractable yield for routine bone samples), the value for pMC aver-ages 0.020 0.16, which suggests that our bone background subtraction is accurate.

Since the limit for reporting finite 14C ages is reached at twice the total standard error () for an indi-vidual 14C measurement (Stuiver and Polach 1977), Tmax (the maximum determinable age) is

strongly influenced by measurement precision. Increasing routine measurement precision, coupledwith modifications to both the breadth and regularity of sample-specific standards described above,has resulted in a reduction in the value for Tmax. Initial testing of the new Oxford HVEE AMSshowed that the system is capable of measuring the 14C/13C and 14C/12C ratios at a precision of up to0.2% (Bronk Ramsey et al. 2004b). The scatter of results for known-age materials, such as treerings, at this level of precision is not higher than the reported standard error. This shows that thequoted errors are not being overestimated. One in every 20 samples dated at ORAU is duplicatedfrom the beginning of pretreatment chemistry, which provides a reasonable assessment of routinereproducibility and, ultimately, a test of whether or not quoted precisions are justified. Bronk Ram-sey et al. (2004b) showed that the reproducibility of repeat measurements on standards matchedclosely the uncertainties ( values) quoted. To achieve a determination of >50 kyr BP, the measure-ment precision must be better than, or equal to, 0.1 pMC (Figure 2). Ultimately, of course, the lim-iting factor in terms of dating samples of bone to ~50 kyr BP is sample-specific rather than instru-

ment or measurement related and requires the elimination of small amounts of more moderncontamination. Evidence collected since ultrafilters were included in the pretreatment of bone atOxford suggests that this technique is a significant improvement in the AMS dating of this material.


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METHOD

Ultrafiltration pretreatments have been tested upona number of important European Middle andUpper Paleolithic bone samples, many of which have been dated before in Oxford or other labora-tories, using other pretreatment chemistries. Initial results reported recently (Bronk Ramsey et al.2004a; Jacobi et al., forthcoming) showed that ultrafiltration appeared to remove contaminating car-

bon more effectively than other methods and produced dates that were often older than those pre-pared using less rigorous methods. In many instances, determinations suspected of being aberrantbecause of their unexpectedly young age with respect to stratigraphy or cultural attribution wereredated using ultrafiltration. These initial Oxford dates were pretreated using 1 of 3 methods:

1. Purified amino acids (ORAU laboratory code AC). The bone was decalcified, and the insolubleresidue was hydrolyzed and treated with activated charcoal before the separation of the aminoacids from inorganic solutes with cation-exchange columns and Dowex 50W-X8 resin(Gillespie et al. 1984; Gillespie and Hedges 1983); this method was used prior to 1989.

2. Ion-exchanged gelatin (code AI). The bone was decalcified, usually with a continuous-flowapparatus (see Law and Hedges 1989; Hedges et al. 1989b). A sodium hydroxide wash wasapplied to partially remove humic contaminants. The insoluble collagen was gelatinized andpurified using an ion-exchange column with BioRad AGMP-50 resin. This method was used

until 2000. It was abandoned because of concerns regarding the possibility of column resinbleed and the difficulty in excluding this as a potential contaminant (see also Burky et al. 1998).

3. Gelatin (code AG). After decalcification, pH3 water was added to a 20-mL sample tube and thecollagen heated at 75 C for about 20 hr. The tube was centrifuged to collect supernatants andfiltered using a 9-m Eezi filter. The gelatin was lyophilized prior to dating. This method has

Figure 2 pMC plotted against pMC error. Each point is a14

C measurement in pMC dated at ORAU over the last15 yr 50 kyr BP, a precision of 0.1 pMC is required.The diamonds are ultrafiltered gelatin determinations. This figure shows an increase in the number of these com-pared with other measurements of ion exchanged (black circles) and gelatin determinations (open squares). Ourconclusion is that this is due principally to 1) the increased levels of measurement precision produced since theinstallation of the new HVEE accelerator (see text) and 2) the introduction of ultrafiltration in the routine pretreat-ment of bone, improving the removal of contaminants in very old bone material.


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been used since 1997 and is still occasionally applied, mainly for modern samples or samplesof very small starting weight.

The ultrafiltration pretreatment method is coded AF in our laboratory. These codes are used in the

tables throughout this paper. Asterisks (e.g. AF*) denote the addition of a solvent pre-wash step(usually using methanol and chloroform). AMS dates of bone of known age using a solvent extrac-tion have shown, when compared with the same bones dated without one, no significant differencesin age. We use a solvent wash on bone suspected of being conserved or glued.

BONE FROM MARINE OXYGEN ISOTOPE STAGE (MOIS) 5 OR 4

Currant and Jacobi (1997, 2001) have identified a cool climate, low species-diversity fauna domi-nated by bison (Bison priscus) and reindeer (Rangifer tarandus) asoccurring at a large number ofLate Pleistocene sites in England and Wales. Dating evidence is sparse, but at Stump Cross Cavernin North Yorkshire a fauna of this type is dated by U-series determinations to the latter part ofMOIS 5 (Baker et al. 1996), and a similar age has been proposed for a fauna from Cassington, nearOxford (Maddy et al. 1998) (Figure 3). It has been suggested (Currant and Jacobi 2001) that this

Figure 3 Location of British sites mentioned in this paper

Church Hole

Pin Hole

Windy Knoll

Uphill Quarry

Robin Hood Cave

Hyaena Den

Kent's Cavern

Hunter's Lodge Inn Sink

0 100km

Banwell Bone Cave

Ash Tree Cave

Steetley Quarry

Bench Quarry

Brean Down

CoyganCassington

Stump Cross Cave

Paviland

Creswell Crags sites

West Pin Hole (Dog Hole)


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fauna may have persisted into MOIS 4, but this is uncertain. In either case, we would expect 14Cdeterminations on bones from these faunas to be beyond the 14C limit. In Table 1, previously datedsamples of bones from faunas of this type are listed. They include finite results.

Samples of bone from Ash Tree Cave and Windy Knoll (Derbyshire), Steetley Quarry (Nottingham-shire), Hunters Lodge Inn Sink (Somerset), and Banwell Bone Cave and Brean Down (North Som-erset) have been dated (Figure 3; Tables 1 and 2). These data show that where samples of bone fromthis fauna have been redated using ultrafiltration, the results are almost always greater than agesand substantially older than previously thought. This both confirms the suspected great age of thisfauna and suggests that earlier finite AMS analyses of this fauna were inaccurate. The application ofultrafiltration techniques improves the removal of trace contaminants and consequently reduces themeasured 14C ages.

THE BRITISH LATE MIDDLE PALEOLITHIC

Pin Hole

The first archaeological site examined in this paper is the cave of Pin Hole, in Creswell Crags gorge,Derbyshire (Figure 3). The samples are all from the lower of 2 cave-earths, investigated by LeslieArmstrong between 1924 and 1936. The artifacts from this sediment are all Middle Paleolithic, andwe would therefore expect ages of >~40 kyr BP. Previous uranium-series and electron spin reso-nance (ESR) dates from the site have supported this conclusion (Jacobi et al. 1998). A series of ion-exchanged gelatin 14C dates (Hedges et al. 1989a) produced a minimum age for the fauna from the

Table 1 AMS 14C determinations of bones from Banwell Bone Cave mammal assemblage-zone sitespreviously AMS dated in Oxford. AF denotes ultrafiltered gelatin determinations, AG denotes a fil-tered gelatin determination, and AI denotes ion exchanged gelatin, as described in the text. Stableisotope ratios are expressed in relative to vPDB and nitrogen to AIR. Mass spectrometric precisionis 0.2 for carbon and 0.3 for nitrogen. Wt% coll. is the amount of collagen extracted as a per-centage of the starting weight. Pretreat. yield is the weight in milligrams of the freeze-dried, ultra-filtered gelatin or ion-exchanged gelatin product, depending on the pretreatment method. CN is theatomic ratio of carbon to nitrogen. %C is the percentage of carbon in the combusted ultrafiltered gel-atin. Each ultrafiltered determination is a direct re-date of the previous sample given above it. In thetables that follow, asterisks in the pretreatment code column denote a solvent extraction prior to bonepretreatment in order to remove potential conservation materials from the bones prior to dating, asdescribed earlier in the text.

Element/speciesOxA-number 14Cage BP Method CN 13C 15N

Wt%coll.

Pretreat.yield (mg) %C

Windy Knoll, Derbyshire

Bison priscus ,radius

OxA-4579 37,300 1100 AI 20.1 1.4 6.8 61.8

OxA-15001 >51,700 AF 3.2 20.8 4.6 10.1 94.5 42.6Steetley Quarry, NottinghamshireBison priscus ,metacarpal

OxA-2846 >44,700 AI 22.2 8.3 25 44.1OxA-15000 >53,200 AF 3.2 20.6 9.4 2.7 14 43.3

Brean Down, North Somerset

Canis lupus,humerus

OxA-4582 41,200 1600 AI 19.8 1.5 5.0 48.0OxA-15002 >52,700 AF 3.2 19.5 10.5 1.7 12.1 41.8

Ash Tree Cave, Derbyshire (clay)

Bison priscus ,cervical vertebra

OxA-7736 >41,500 AG 3.3 20.9 5.6 6.2 75.6 31.2OxA-15003 >57,700 AF 3.2 20.6 6.6 2.6 25.6 42.1


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same levels as the Middle Paleolithic artifacts of ~40 kyr BP (Table 3) (Jacobi et al. 1998). Howmuch older the fauna and the archaeology might be remained largely unresolved, although the U-series dates suggested that the sediments in which these occurred were more recent than ~64 kyr BP(Jacobi et al. 1998). The resolution of this problem could be addressed using a new dating programinvolving improved pretreatment chemistry. This new series is shown in Table 3 and illustrated inFigure 4. The results reported here expand on those in Jacobi et al. (forthcoming).

Ultrafiltration has resulted in older, and sometimes substantially older, results, some of which are>50 kyr BP. It is noticeable that what in several cases were infinite ages have now become finite.This suggests that ultrafilters are more effectively removing the kind of contaminants that previousmethods were not. Dates obtained previously in Oxford using ion-exchanged gelatin (Hedges et al.1989a) were underestimates of the true age.

In the absence of cut-marked and human-modified bone from this site, there is no possibility of fur-ther refining the age of its occupation by Neanderthal humans. The same problem applies to theadjacent site of Robin Hood Cave, where a broadly similar chronology has been obtained for itsMiddle Paleolithic archaeology (Jacobi et al., forthcoming).

Coygan Cave

Coygan Cave, now quarried away, overlooked Carmarthen Bay in South Wales (Figure 3). It wasinvestigated several times during the 19th and 20th centuries, the most recent excavations in 196364 being directed by John Clegg and Charles McBurney. It is from this excavation that dating sam-ples have been obtained. The site is of importance for yielding evidence of use by Middle Paleolithichumans and, more extensively, for denning by spotted hyaenas (Crocuta crocuta: Aldhouse-Greenet al. 1995).

Dating of flowstones by Henry Schwarcz suggested that the cave had been closed for much of theLate Pleistocene, only reopening some time after ~64 kyr BP (Aldhouse-Green et al. 1995). Apartfrom a single small piece of carbonized large-mammal bone, there is no human-modified bone fromthe cave, so human presence remains undated. There are, however, 5 dates on bone and tooth thatdirectly date hyaena activity in the cave and, by association, date when the cave could have beenopen for human occupation (Table 4). Each sample included ultrafiltration in its pretreatment, and it

Table 2 AMS 14C determinations of bones from Banwell Bone Cave mammal assemblage-zonefaunas excavated from the sites of Ash Tree Cave, Banwell Bone Cave, and Hunters Lodge InnSink. All analyses are ultrafiltered determinations. See the Table 1 caption for details of the other

analytical information. indicates duplicate determinations.

Element/speciesOxA-number 14C age BP CN 13C 15N

Wt%coll.


Ash Tree Cave, Derbyshire (clay)

Bison priscus, metatarsal 13800 >54,100 3.3 20.4 8.8 3.7 30.0 46.8Bone fragment 13801 >56,500 3.3 20.4 9.9 6.4 47.7 47.1Bone fragment 13802 52,800 3100 3.3 20.2 10.0 2.4 17.0 43.3Banwell Bone Cave, North Somerset

Bison priscus, calcaneum 14136 >59,500 3.2 20.3 10.8 14.8 59.0 41.2Bison priscus, calcaneum 14137 52,700 1900 3.2 20.6 11.1 6.0 35.0 41.7

14138 >53,900 3.1 20.7 10.6 3.5 14.6 41.1Hunters Lodge Inn Sink, Somerset

Bison priscus, scapula 13566 >54,800 3.2 20.6 8.8 3.6 17.9 43.2


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is noticeable that all are considerably older than a determination obtained in 1990 for a hyaena-gnawed radius of woolly rhinoceros of 24,620 320 BP (OxA-2509: Hedges et al. 1994). Thisdetermination was 43,000 3.2 19.7 n.d. 0.7 43AF 13880 52,500 2800 3.3 19.8 3.5 3.5 43

50/70 Coelodonta antiquitatis,right P4

AI 4429 >42,300 19.2 8.4 51AF 13881 45,000 750 3.2 19.2 4.7 5.0 45

50/80 Equus ferus, incisor AI 4430 44,900 2800 20.2 7.3 51AG 13590 44,300 2100 3.1 20.9 5.9 3.5 41

AF 13889 47,000 1200 3.2 20.8 3.9 4.6 4250/100 Coelodonta antiquitatis, ulna AC 1813 >41,400 21.0 10.8 23AF 12808 54,000 2900 3.2 20.1 2.4 4.1 42

53/76 Bovini, left radius/ulna AI 4427 >44,200 18.7 5.5 55AF 13591 48,000 1000 3.1 19.8 6.6 11.0 43

62/90 Equus ferus,metapodial fragment

AF 11978 53,000 1900 3.2 20.6 5.6 6.4 41

64/70 Rangifer tarandus, antler AF 11796 44,200 800 3.3 17.5 1.6 4.5 41

64/90 Equus ferus, right navicular AF 11977 49,600 1000 3.3 20.6 4.0 11.6 42

64/110 Coelodonta antiquitatis,right radius

AF 11979 >51,400 3.3 19.7 3.4 7.1 41AF(


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THE BRITISH MIDDLE TO UPPER PALEOLITHIC

Kents Cavern

The site of Kents Cavern (Torquay, Devon) is one of the most important Paleolithic sites in Britain.The oldest human fossil from SW England, a fragmentary human maxilla, comes from here and wasexcavated in March 1927 (KC4: Oakley et al.1971). Its context was in cave-earth at a depth of 106in an excavation against the north wall of the Vestibule, the entrance chamber to the cave. This wasdirectly dated at Oxford in 1988 and gave an age of 30,900 900 BP (OxA-1621: Hedges et al.

Figure 4 Comparison between initial AMS dates from Pin Hole, pretreated using ion-exchanged gelatintechniques (squares) and a new series based on ultrafiltration (circles). The results are presented in orderbased on distance into the cave from the datum point at the entrance.

Table 4 14C determinations from Coygan Cave, South Wales. As indicated previously, all asterisksdenote a solvent extraction prior to collagen pretreatment. The failed samples were mistakenly notsolvent-extracted and therefore failed. These will be resampled in the near future. See the Table 1caption for other analytical details.

Samplereference Species/element

Pretreat.code

OxA-number 14Cage BP CN 13C 15N

Wt%coll. %C

Spit 1 1108 C. crocuta C AF* 14400 32,140 250 3.2 18.6 11.2 4.8 49.2Spit 1 1109 C. crocuta C AF* 14401 43,000 2100 3.2 18.3 10.7 1.0 49.2Spit 4 1037 C. crocuta P3 AF FailSpit 5 1049 C. crocuta M1 AF* 14473 32,400 550 3.3 19.1 9.6 1.6 35.3Spit 5 1059 C. crocuta

left dentaryAF Fail

Spit 6 1070 C. crocuta I3 AF* 14402 36,000 500 3.2 18.3 11.6 3.4 50.4Spit 7 1078 C. crocuta P3 AF* 14403 39,700 1700 3.3 17.3 10.8 1.3 45.4


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1989a:209). The specimen is so fragmentary that it is uncertain whether the human represented pos-sessed an anatomically modern morphology or was a Neanderthal. This problem may be resolved byan analysis of the DNA signature of the specimen. Questions also arise regarding the reliability ofthe AMS date because it is now apparent that the maxilla had been treated with a thin, water-solubleglue. Further AMS dates using ultrafiltration have therefore been obtained to constrain the age of themaxilla more reliably. The bones and teeth dated come from directly above and beneath its find con-text (Table 5).

Once again, ultrafiltered gelatin ages are older than those previously obtained. This is particularlythe case with the cranial fragment of woolly rhinoceros found only a short way above the maxilla(compare OxA-6108 and -13965). The pair of woolly rhinoceros metacarpals (3 and 4) articulate,and the agreement between the ages for these 2 bones indicates acceptable reproducibility. The lioncanine produced a very low yield (0.44 wt% collagen), so the standard error was larger than ideal.

Table 5 AMS 14C determinations from Kents Cavern. See the Table 1 caption for details of the ana-lytical information and the text for information regarding the pretreatment codes. Results are pre-sented in increasing depth below the datum, which is the granular stalagmite. Note that the 13Cvalue for OxA-1621 is not a measured value but an estimate. The correct value ought to be closerto 19 2. We have not recorrected the original AMS date to this value since there is no actual stableisotope measurement, and the correction will not result in a substantially different result. The deep-est Upper Paleolithic artifact from this trench is at 15. In closely adjacent trenches excavatedbetween 1934 and 1938, and using the same datum, Middle Paleolithic artifacts were recovered

from depths between 139and 176. There is, therefore, the possibility of an overlap betweenEarly Upper Paleolithic and Late Middle Paleolithic materials in the lowest part of the Upper Pale-olithic range. This is taken to be the explanation for the older 14C determinations in this tablebetween 133and 15. OxA-14761 was duplicated as part of ORAUs internal QA program at47,700 3700 BP.

Depth Element/speciesPretre.code

OxA-number 14C age BP CN 13C 15N

Wt%coll. %C

83 Coelodonta antiquitatis,right metacarpal 3

AI 3450 34,620 820 19.7 1.0 42.5AF* 13921 36,040 330 3.4 19.6 6.4 5.5 36.6

83 Coelodonta antiquitatis,right metacarpal 4

AI 3449 34,500 800 19.3 3.9 41.0AF* 14210 36,370 320 3.3 20.1 7.1 6.0 44.5AF* 14701 35,650 330 3.3 19.4 7.4 5.8 43.6

90 Ursus arctos, left dentary AF* 14059 35,600 700 3.2 19.0 11.5 0.95 41.7

96 Coelodonta antiquitatis,cranial fragment

AI 6108 30,220 460 20.0 2.3 42.4AF 13965 37,200 550 3.2 20.1 6.2 2.6 40.2

106 Homo sp., right maxilla AC 1621 30,900 900 26.0 1.7

1213 Coelodonta antiquitatis,distal right tibia

AF* 14715 35,150 330 3.3 19.4 6.5 3.44 41.8

133 Panthera leo, left C AF 14285 43,600 3600 3.2 17.4 13.3 0.44 54.7

140 Coelodonta antiquitatis,left unciform

AF* 14761 45,000 2200 3.4 19.9 6.4 1.7 42.0

150 Rangifer tarandus,left dentary

AG* 13589 37,900 1000 3.1 18.9 7.1 1.5 41.4AF 13888 40,000 700 3.3 18.5 5.1 2.8 41.9

1920 Rangifer tarandus,proximal radius

AF* 14714 49,600 2200 3.3 18.6 5.4 3.1 40.3


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The new results suggest that the previously obtained age for the maxilla was a severe underestimateand that its most likely age is, instead, between 3537 kyr BP. This makes even more tantalizing theproblem of its attribution. The artifacts found with the maxilla are very few but are clearly UpperPaleolithic; however, they cannot be culturally diagnosed. The deepest sample, the radius of rein-deer (OxA-14714), was found deeper than any archaeological finds in this part of the cave, whichincludes Middle Paleolithic as well as Upper Paleolithic artifacts.

Uphill Quarry and the Hyaena Den

Recent researchers tend to correlate the spread of anatomically modern humans with an Aurignaciantechnology (Bocquet-Appel and Demars 2000; Kozlowski and Otte 2000; Davies 2001; Conard andBolus 2003; Mellars 2004a,b). This suggestion makes the direct dating of the Aurignacian of con-siderable interest. For Britain, 2 artifacts assume importance in this context: a lozangic bone/antlerpoint from Uphill, near Weston-super-Mare (North Somerset), and a bone/antler point from theHyaena Den at Wookey Hole (Somerset), some 25 km to the west (Figure 3).

The Uphill point was dated in 1999 using filtered gelatin and produced an age of ~28 kyr BP (Jacobi

and Pettitt 2000) (Table 6). This would have implied an Aurignacian presence at, or very close to,the time when 14C determinations indicate that a Gravettian technology may have been in existencein Belgium (Vrielynk 1999; Haesaerts and Damblon 2004). Davies and Gollop (2003) suggestedthat, if reliable, this would imply Aurignacian humans living in an area of extensive contemporarysnow cover, which was unlikely. This specimen was therefore redated using ultrafiltration in 2004.

Once again, the new age is substantially older than the previous gelatin age (Table 6). The point istherefore contemporary with the Aurignacian II as defined for SW France on the basis of lithicindustries (Djindjian 1992). This correlates well with the sparse typological clues that can bededuced from Aurignacian lithic artifacts found at other sites in the British Isles, e.g. Paviland on theGower coast of South Wales.

The point from the Hyaena Den was found between 189095 by Edward Brooks in a part of the cavewell away from the Middle and Early Upper Paleolithic (Jerzmanowician) artifacts for which thesite is better known. It is similar to points from Aurignacian contexts, such as La Ferrassie (Hahn1988: Figure 3.4) and the Abri Blanchard (Leroy-Prost 1979: Figure 86.8). Bone from this point was

Table 6 14C determinations of the Aurignacian lozenge-shaped point from Uphill(Bristol City Museum BRSMG Ce 16476 Up). OxA-8408 was reported previouslyby Jacobi and Pettitt (2000). See Table 1 caption for analytical details.

OxA-number Method 14C age BP CN 13C 15N

Wt%coll. %C

8408 AG 28,080 360 3.3 17.3 1.0 9.1 35.013716 AF 31,730 250 3.2 17.5 1.2 9.4 43.7

Table 7 14C determination of a Paleolithic bone or antler point from the Hyaena Den. See Table 1caption for analytical details.

OxA-number Method 14C age BP CN 13C 15N Wt% coll.


3451 AI 24,600 300 n.d. 20.1 n.d. 0.96 2.4 45.8

13803 AF* 31,550 340 3.4 19.2 2.3 2.0 11.7 41.8


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first dated in 1991 using the ion-exchanged gelatin method (Table 7). Archaeologically, the resultimplied a Late Gravettian age with human presence in Britain at a time of lowering temperatures.The ultrafiltered age obtained is again significantly older, confirming its likely cultural attribution tothe Aurignacian. The ages for both of these points are intriguingly similar, perhaps documenting theactivities of the same human group. The sites are linked by the River Axe.

THE FRENCH EARLY UPPER PALEOLITHIC

In the light of the results described above, the current work has been extended to the importantFrench Paleolithic sequences derived from sites in the Dordogne, including La Ferrassie and theAbri Pataud (Mellars and Bricker 1986). These sites have been selected for reinvestigation becausetheir chronologies are so often cited in discussions of the Early Upper Paleolithic in western Europeand the spread of anatomically modern humans. Comparisons are often made with their lithic indus-tries when assessing the age of other sites. For both sites, the new dates once more suggest that thepublished chronologies are underestimates of the true situation.

The freshly dated material consists of bone obtained from amongst material previously submitted by

Prof Paul Mellars (Cambridge University) and archived at ORAU. The first sample is from the AbriPataud, which was excavated by Movius (1975, 1977). The locality is one of the most extensively14C-dated Early Upper Paleolithic site in Europe, with 34 dates from the Groningen laboratory andanother 16 from Oxford, all obtained prior to the 1990s.

There are 14 cultural levels at this rock shelter. The newly dated bone was selected because of theclear cut-marks visible on its surface and is from level 13 (Table 8), the lowest but one of the Aurig-nacian layers. The date obtained is the oldest for the Aurignacian at this site and suggests that pre-viously dated burnt bone samples from around and beneath the level of this sample are likely to beunderestimates of the true age by ~2000 14C yr. This is of considerable interest for confirming howearly anatomically modern humans may have been present in this area. More work is planned.

The dating of the archaeological levels at the nearby site of La Ferrassie has been more complicated.A large series of dates from the Gif-sur-Yvette laboratory produced dates that, in many instances,were younger than those initially produced in Oxford. OxA-402 to -404, for instance, are older thanGif dates obtained from the same levels (Gowlett et al. 1986:214; Mellars and Bricker 1986: Figure2). However, our reanalysis shows that these Oxford dates are also likely to be underestimates.

Samples obtained by Mellars from the excavations of Delporte (1984), and archived at ORAU, werereexamined. Two samples of large herbivore bone were selected for dating, one of which was clearlycut-marked (OxA-15218). The other had been previously dated (OxA-403). The ultrafiltered repeatdate was again significantly older (OxA-15217; Table 8). The date for OxA-15218 comes from oneof the levels designated by Delporte (1984) as Aurignacian II. The sample from level D2h is from alevel with early Gravettian Font-Robert points and is the oldest determination for an industry of thistype. Again, further work is proposed to expand on these results.

THE RUSSIAN EARLY UPPER PALEOLITHIC

It is important to emphasize that by no means have all of the Paleolithic bone determinations wereanalyzed produced older 14C ages. The majority of low yielding and/or contaminated bones tendto follow this pattern, but where bone is reasonably well preserved, gelatinization is likely to be aneffective pretreatment. An important redated human bone sample from Russia illustrates this pointwell.


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The human remains come from the 3rd cultural layer of Kostenki 1, which is attributed to the Aurig-nacian. Kostenki 1 is in Russias Voronezh region and is the most easterly site of this industry yet

identified. The bone was excavated by Dr Andrei Sinitsyn (Sinitsyn 2003). The gelatin dateobtained in 1997 from a human femur was reanalyzed using ultrafiltration and both results are sta-tistically indistinguishable from each other (Table 9). The standard error of the new determination,however, is substantially reduced. The second Aurignacian assemblage within the immediate area(Kostenki 14 [Markina gora]) has a charcoal determination of 32,420 +440/420 (GrA-18053) (Sin-itsyn, personal communication).

This result demonstrates that not all Paleolithic bone dates obtained using an AG pretreatment areproblematic. The major shifts in age identified above tend to be associated with those bones produc-ing often very low collagen yields or those that were probably contaminated, or both. This is wellillustrated in the next section.

FAILED BONES

A number of hyaena teeth that were initially dated using gelatin or ion-exchanged gelatin techniqueshave been reanalyzed using ultrafiltration and have failed because sufficient collagen could not beobtained. In these cases, it is suspected that the initial determinations are probably unreliable, sincedoubts are cast upon the preservation state of the bone collagen, which increases the possibility forcontamination to be significant in its influence.

Samples falling into this category include: OxA-5798 (25,660 380 BP) was an ion-exchanged gelatin date on a hyaena tooth from Ash

Tree Cave (Derbyshire). We pretreated and ultrafiltered 370 mg of dentine redrilled anew fromthis specimen but obtained 0 mg yield. We suspected the original date to be erroneously youngfrom its stratigraphic context.

Table 8 New 14C determinations (AF* codes) reported from the Abri Pataud and La Ferrassie.13Cvalues for all AC determinations are estimated.OxA-15217 is a repeat of OxA-403.OxA-

number Sample ref. Method14

C age BP CN 13

C 15

N % coll.

P. yield

(mg) %CAbri Pataud15216 AF* 35,400 750 3.2 18.7 7.6 1.23 7.63 41.46La Ferrassie401 AC 23,800 530 26402 AC 27,900 770 26

403 F.70.56. D2h. 54 AC 27,530 720 2615217 AF* 29,000 370 3.2 19.3 5.7 1.18 7.06 40.0

404 AC 26,250 620 26405 AC 29,000 850 2615218 F.72.54.K3 156 AF* 33,610 340 3.2 18.4 6.8 2.63 15.75 40.2

Table 9 Bone determinations from Kostenki 1, Russia.

OxA-number Method 14C age BP CN 13C 15N

Wt%coll.

P. yield(mg) %C

7073 AG 32,600 1100 3.0 18.2 15.8 3.6 20.2 41.215055 AF 32,070 190 3.2 18.5 14.8 9.6 144.0 38.1


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OxA-5800 (24,000 260 BP) was a date for a hyaena incisor from Church Hole (on the Not-tinghamshire side of Creswell Crags gorge). This determination is among the youngest of anyhyaena dated in the British Isles. The tooth was originally selected for dating because all of theother hyaena material from Church Hole was treated with glue. The original ion-exchanged gel-atin date produced a yield of 2.0 mg from 340 mg of dentine. We attempted to redate this spec-imen, but the remaining material consists almost completely of tooth enamel that has beenshown to be problematic for 14C dating (Hedges et al. 1995). The sample was therefore failed.

OxA-5801 (33,450 700 BP) was a date for a hyaena tooth from Late Glacial sediments out-side the west entrance to Robin Hood Cave (Derbyshire). The initial ion-exchanged date com-prised an analyzed sample of 500 mg of dentine from which 10.4 mg of collagen was obtained.The determination appears to be suspicious since the reanalysis using ultrafiltration resulted ina 0.6-mg ultrafiltered gelatin yield from a 405-mg dentine starting weight. This reanalysis wastherefore considered failed due to this low yield.

OxA-6114 (22,980 480 BP) was an incisor recovered in 1981 from a small excavation in thesouthwest corner of the Western Chamber of Robin Hood Cave. Middle Paleolithic artifactswere recovered at this time. Fresh dentine was drilled from the tooth (143 mg) but produced a

0-mg yield of collagen after being ultrafiltered. OxA-5803 (29,300 420 BP) was a date of dentine from a hyaena tooth found in the spoil fromWest Pin Hole (Dog Hole), Creswell Crags (Derbyshire). Our reanalysis of this sample resultedin a 0-mg collagen yield from 106 mg of dentine.

These failures suggest strongly that the initial dates ought to be considered problematic, since theattempts to redate the samples show that there is little or no recoverable collagen of acceptable qual-ity in the teeth. These 14C results ought to be set aside from serious consideration in the archaeolog-ical literature. Convincing evidence in support of this conclusion comes from 2 hyaena teeth fromthis initial series that did produce very small amounts of extractable ultrafiltered collagen butyielded substantially different ages (Table 10).

CONCLUSIONS

14C-dated bones that contain a proportion of undegraded collagen generally produce reliable andaccurate determinations, which can be validated where appropriate analytical data are collected andadequate purification techniques are applied. 14C dating of bone that is low in collagen is much more

Table 10 14C determinations of hyaena teeth from Church Hole and Robin Hood Cave,

Creswell, Derbyshire. See Table 1 caption for analytical details.OxA-number Method 14C age BP CN 13C 15N

Wt%coll.


Church Hole Cave (CHC20-24, CC3, tooth, Crocuta crocuta)

5799 AI 26,840 420 20.6 0.31 1.1 34.514926 AF >40,000 3.2 18.8 11.3 1.62 2.4 42.5Robin Hood Cave (RH121-132, 1969, OB,16,197, CC6, tooth, Crocuta crocuta)

5802 AI 31,050 500 19.1 1.79 5.0 36.014944 AF >49,800 3.2 18.8 12.8 2.16 8.5 43.9Robin Hood Cave (RH1238 1981 excavation A spit 26, tooth, Crocuta crocuta)

6115 AI 22,880 240 20.8 2.87 15.5 43.512736 AF >52,800 3.1 18.1 9.2 3.47 12.5 43.5


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challenging and sometimes can result in erroneous determinations (for this reason, ORAU does notdate bone below 1-wt% collagen or 10-mg collagen pretreatment yield, unless circumstances areexceptional). For these types of bones, it is crucial that both rigorous purification techniques areapplied and adequate screening methods are routinely implemented. The AMS dating of bone fromthe Middle and Upper Paleolithic periods has considerably improved with additional pretreatmentusing ultrafiltration, judging by the results presented here. Some workers (e.g. Jris et al. 2003) havenoted that where charcoal and bone are dated from identical contexts in Paleolithic Europe, boneoften produces younger ages by comparison. Our results show that, once again (see also Brown etal. 1988; Hedges and van Klinken 1992), ultrafiltration often increases the measured age comparedwith simple gelatinization and could, in part, contribute to the resolution of this problem. In addi-tion, ultrafiltration effectively acts as a screening method by eliminating bone of dubious quality,that is, bone that has a low yield of recoverable collagen of sufficient quality. Ultrafiltration will notremove contaminants greater in molecular weight than the molecular weight cut-off of the filters, sohigher mass contaminants, such as unbroken cross-linked humic complexes, will not be removed(see also van Klinken and Hedges 1995). However, the potential problems associated with thesetypes of samples can be minimized by the routine collection of a suite of subsidiary analytical data

(see Hedges and van Klinken 1992; van Klinken 1999), such as those given in the tables of thispaper. The reliability of some previous Oxford ion-exchanged gelatin determinations is questioned.For some of these determinations, it is possible that the presence of resin from column bleed may bean equally important influence, particularly in those cases where pretreatment yields were very low.

Other factors are crucial in contributing to the general improvement in dating bone from this period.The background limit of 14C dating bone has been demonstrably reduced over recent years inOxford. Improved AMS instrumentation and measurement precision and the use of a battery of bonestandards of infinite and finite age similarly contribute. The dates obtained on Paleolithic bone ingeneral make much more archaeological sense when compared with those previously dated. Adetailed reanalysis of ages from the European Middle to Upper Paleolithic record is clearly required,and it is to this end that we are now working.

ACKNOWLEDGMENTS

We thank the Leverhulme Trust-funded Ancient Human Occupation of Britain (AHOB) projectand the NERC-AHRC Oxford Radiocarbon Accelerator Dating Service (ORADS) for providingfunding for this work. We thank the staff (past and present) of the Oxford Radiocarbon AcceleratorUnit, University of Oxford, for their careful analytical preparation and AMS work. Dr Alistair Pike(Bristol) and Tony Jarratt (Wells, Somerset) have allowed us to quote results from Ash Tree Cave,Banwell Bone Cave, and Hunters Lodge Inn Sink, respectively. We thank Prof Paul Mellars (Cam-bridge) for permission to redate the French material and Dr Andrei Sinitsyn (St Petersburg) for per-mission to report the new Kostenki date. Silvia Bello (AHOB) produced the map for us. Weacknowledge with gratitude the many museum curators who have collaborated with us in thisproject. We acknowledge useful discussions and comments from Dr Tom Brown (LLNL Center forAccelerator Mass Spectrometry, University of California, Livermore).

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